Wireless charging is an evolving technology that may bring great convenience to charging millions of electronic devices. Wireless charging for electric toothbrushes is one of the most typical applications. Due to the water resistance and electrical safety requirements, the batteries of modern electric toothbrushes are usually hermetically sealed inside of their handles. Therefore, wireless charging becomes the most suitable and convenient way to recharge the sealed batteries.
In an electric toothbrush wireless charging system, energy is transferred from a power transmitter to one or multiple power receivers, via a pair of coupled magnetic coils, one disposed in the transmitter and the other in the receiver. The charging efficiency, which is the ratio of the received power by the receiver over the transmitted power from the transmitter, is the most critical parameter in wireless charging. Improving the charging efficiency will effectively reduce the energy wasted during transmission, and prevent heat discharges or over-voltage damages to the charging devices. Also, the improved efficiency could eliminate unnecessary electromagnetic radiations, preventing potential radiation effects to human bodies.
Most of the electric toothbrush products, such as Philips Sonicare Diamond Clean or Oral-B P7000, are equipped with the wireless charging features. However, these conventional systems cannot tune the transmitter power during a charging process, e.g., in situations when the battery becomes fully charged or when the brush is moved, so the charging efficiency is not optimized.